A "unit load" may be defined as a single item, e.g., a piece of equipment, such as an offset duplicating machine, or a collection or items, e.g., a rack of glass panes, that is to be moved from one location to another. Frequently, the unit load is both heavy and fragile.
Manipulating a unit load, e.g., the piece of equipment, may include shipping the equipment to a particular destination, positioning it in a desired location, and lowering it to a foundation surface, such as the ground, a floor, a platform, or the like. Considerable care is required to avoid damage to either the equipment or the people manipulating the equipment. A blow to the equipment can cause structural damage or upset delicate factory settings. Dropping the equipment may not only similarly damage the equipment but may also endanger people close to the equipment.
Conventional devices for manipulating a unit load have several drawbacks. For example, U.S. Pat. No. 4,079,907 discloses a cushioned shipping support which includes a bumper-skid having a wedge-shaped portion. Similarly, U.S. Pat. No. 3,602,376 discloses a self-unloading skid having corner feet with an inclined slip plane. In each of these conventional devices, the unit load is shipped while resting on the skid and then lowered into position by sliding the unit load down the incline of the skid.
However, the rate at which the unit load slides off the skid is frequently not accurately predictable because it depends on a number of inter-related factors including the angle of the incline, the amount of friction between the skid and the equipment, and the weight of the unit load. For example, if the skid becomes wet during shipping, the unit load may slide down the incline at an excessive rate because the friction between the skid and the unit load may be greatly reduced if the incline is wet.